1. Field of the Invention
The invention relates generally to video displays. More specifically, it relates to updating the data used in video displays.
2. Description of the Related Art
Most modem display devices rely on cathode ray tube (CRT) technology, which requires that any illuminated spot on the display must be constantly regenerated, or refreshed, to keep it from fading away. To avoid the perception of flicker, the entire image is typically refreshed (redrawn) at least 60 times per second, and 75–85 times per second is common. For a high-resolution digital color image, these considerations may require that a signal containing the equivalent of hundreds of millions of bits per second of video data be continuously delivered to the CRT to keep the image on the display screen. This is true even if the image is static, meaning the image itself does not change.
FIG. 1 shows a conventional computer-driven display system. Graphics controller 12 contains video memories 17, 19, which contain digitized data representing the images being displayed on displays 16, 18. Graphics controller 12 is co-located with a computer (not shown), so the computer can update the video memories 17, 19 over a standard high-speed data bus. Image data is repeatedly read from video memory 17 and continuously delivered to display device 18 over video cable 14. In a like manner, separate image data is repeatedly read from video memory 19 and continuously delivered to display device 16 over video cable 15. The data traveling through each cable is a serial bit stream or analog signal representing the actual image, and is formatted for the particular display device. Therefore, only one image may be transmitted over a particular cable and separate cables are run if different images are to be simultaneously displayed on different display devices. Separate cables are also run if the same image is to be simultaneously displayed on different types of display devices requiring differently formatted signals. If the display devices are very far from the graphics controller (such as flight status monitors scattered throughout an airport), the cost of running these multiple cables can be excessive. In addition, the graphics controller has separate connectors for each cable and separate video driver circuits for each connector, thus adding to the cost of the graphics controller itself.
In recent years, flat panel displays have begun to replace CRT technology for display devices, allowing image data to be transmitted to the display in different formats than that required by CRTs. However, the nature of the technologies used in flat panels still requires repetitive refresh of the image. Even though the refresh rate for a static image might be improved for a flat panel over that of a CRT, moving pictures require the displayed image to be repeatedly changed for all display technologies, and conventional techniques repeatedly refresh the entire image to accomplish motion in the image.
The need to constantly refresh the entire image creates more expensive graphics controllers, excessive cable requirements, and a large bandwidth requirement between the graphics controller and the display.